The present invention relates to an attaching structure for a ceramics bearing, and more particularly to a structure for attaching to a metal shaft a ceramics bearing which comprises an inner ring, an outer ring and rolling members and in which at least the inner ring is made of ceramics.
Since ceramics are higher than metals in high-temperature strength, roller bearings for use at high temperatures include ceramics bearings comprising an inner ring, an outer ring and rolling members which are all made of ceramics. However, the use of such ceramics bearings involves the following problem because the shaft to which the inner ring is attached is made of metal. Metals are greater than ceramics in coefficient of thermal expansion, and the difference increases with an increase in temperature. Accordingly, if there is no clearance between the metal shaft and the ceramics inner ring at room temperature, a negative clearance occurs therebetween at the operating temperature, with the result that the inner ring is subjected to a tensile stress. Generally, ceramics are not resistant to tension, and the inner ring is likely to break under tension, so that the occurrence of such a negative clearance is considered undesirable. For this reason, it is practice to provide a positive clearance between the shaft and the inner ring at room temperature to preclude the occurrence of a negative clearance at the operation temperature. Nevertheless, the positive clearance causes objectionable creep between the shaft and the inner ring. It is also proposed to provide between the metal shaft and the ceramics inner ring a member for absorbing the difference in thermal expansion between the two materials (Operation of an All-Ceramic Mainshaft Roller Bearing in a J-402 Gas-Turbine Engine, C 324C, Prepr. Presented ASLE Annu. Meet. (Am. Soc. Lubr. Eng.) (U.S.A.) 35th 3C. 1-3C. 7('80)). However, the member, when used, renders the assembly complex in structure and difficult to handle.